Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
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3 records were found.
Polymyxin B prevents the germination of ascospores of Neurospora tetrasperma with an LD50 of 3-4 p.p.m. The toxic effect of polymyxin is partially reversed by calcium and magnesium ions. The effect of polymyxin on the respiration of activated ascospores does not become apparent until after 2 hr. The effect upon respiration is reversed by calcium ions. Dormant and activated ascospores remove about the same amount of polymyxin from solution almost immediately upon exposure to the antibiotic. After 90 min. the apparent uptake of activated cells is markedly diminished while that of the dormant spores increases slightly. Polymyxin competes noncompetitively with methylene blue for sites on the surface of the cells when added simultaneously with the dye. However, if the antibiotic is added before methylene blue, dye uptake is almost entirely ...
A morphological mutant of Neurospora crassa, snowflake, is shown to contain filaments which are about 70 A in diameter, and up to several microns long, and which usually bunch in groups of a few to several hundred. They may be found longitudinally or transversely arranged with respect to the long axis of the cell and, in many cases, they run up to the plasma membrane, but not through it. The filaments often are arranged in crystalline arrays but may also be found as separate filaments. Sometimes the filaments are closely appressed to nuclei and may be found inside them. It is likely that the filaments are not the result of the dissociation of microtubules and are most likely microfilaments like those found in other organisms. Their relationship to the origin of certain morphological mutants in Neurospora is discussed.
The Q 10 for the frequency (number of bands per 24 hours) of the ‘clock’ mutant (strain CL11A) of Neurospora crassa over the range 20–30° C is close to 1.0. By contrast, that for the double mutant, ‘wrist watch’ (strain CL12a), is closer to 2 over this temperature range. Strain CL12a differs from ‘clock’ in other ways as well, including 1) decreased rate of linear extension and band size, 2) greater sensitivity of growth rate to high temperatures and, 3) masking of rhythmic growth below 15° C. The response to temperature of several colonial mutants and standard (‘wild-type’) strains was studied and it is shown that some strains are temperature-independent yet arhythmic. A temperature-compensation model is presented to explain the response of ‘clock’ mutants to temperature and it is concluded that they demonstrate a non-circadian free-r...
